In a nuclear reactor, an inherent shutdown assembly includes a mass of nuclear absorber material located above the core region, sufficient to shutdown the entire system and terminate any dangerous transients. When either the neutron flux or the core coolant temperature exceeds some critical value, a trigger is actuated and this releases a latch permitting the neutron poison mass to be inserted into the core. The poison mass absorbs excess neutrons generated in the core, thereby controlling dangerous transients.
Such an assembly includes means to sense the temperature of the coolant or the neutron flux, means to hold the poison mass in a position above and ready to be released into the reactor core, and means for triggering the release of the poison mass into the core when the sensing means indicates that the critical temperature has been reached or that the neutron flux has reached a critical value. Present devices generally suffer from being one-time-only devices, that is, once they have been activated they can't be used again. This prevents in situ or ex-reactor testing of such devices. An example of such a device is a poison mass which is restrained by a membrane whose melting point is at a critical temperature. When the critical temperature is reached, the membrane melts thus releasing the poison into the reactor core. Since it is a one-time-only device, it cannot be tested to see if it is operating properly prior to the actual failure of the reactor. In addition, present devices have separate sensing, triggering and release elements which encumber design and operation, requiring in many cases external connections to the assembly. In particular, it is desirable to provide a separate sensor trigger element capable of being of small size and of being tested in situ or ex-reactor.
It is therefore an object of this invention to provide an inherent shutdown assembly for nuclear reactor.
Another object of this invention is to provide an inherent shutdown assembly capable of being tested in situ.
Another object of this invention is to provide a sensor trigger for releasing an object into an environment with the temperature or neutron flux of the environment equal to or greater than a critical value.